Continuous process for recovering waxes from oily sludges

ABSTRACT

IN THE FIRST STAGE OF A CONTINUOUS PROCESS OILY SLUDGES ARE MIXED WITH LIGHT HYDROCARBONS DIFFERING SUBSTANTIALLY IN SPECIFIC GRAVITY THEREFROM TO SEPARATE THE SLUDGES INTO AN OIL-HYDROCARBON PHASE A WATER-WAXY SOLIDS PHASE. THE OIL-HYDROCARBON PHASE IS HEATED TO A TEMPERATURE ABOVE THE CRITICAL TEMPERATURE OF THE LIGHY HYDROCARBONS TO REMOVE THE LIGHT HYDROCARBONS WHICH ARE THEN RECYCLED FOR FURTHER USE. THE WATER-WAXY SOLIDS PHASE IS TREATED TO OBTAIN WATER REDUCED CHEMICAL OXYGEN DEMAND WHICH CAN BE DISCHARGED IN RECEIVING BODIES OF WATER WITHOUT POLLUTING THE SAME. THE WAXY SOLIDS-WATER SLURRY WHICH REMAINS IS, IN THE SECOND STAGE OF THE PROCESS OF THIS INVENTION, DIRED AD THE RESULTING DRY WAXY SOLIDS ARE TREATED WITH A LIGHT ORAMITIC SOLVENT SUCH AS BENZENE, TO YIELD A SOLUTION OF WAX AND THE AROMATIC SOLVENT AND WAX-FREE SOLIDS. AFTER THE AROMATIC SOLVENT WAX SOULTION IS STRIPPED TO REMOVE THE AROMATIC SOLVENT, A VALUABLE WAX PRODUCT REMAINS. IN A FINAL STEP, THE WAX-FREE SOLIDS ARE HAETED TO REMOVE THE LAST TRACES OF THE AROMATIC SOLVENT THEREFROM YIELDING DRY, HYDROCARBON-FREE, SOLIDS WHICH ARE SUITABLE FOR A WIDE VARIETY OF USES, SUCH AS, FOR EXAMPLE, FOR LAND FILL.

Jill. 16 1973 COLE ET AL 3,711,400

CONTINUOUS PROCESS FOR RECOVERING WAXES FROM OILY SLUDGES Filed Nov. 6,1970 United States Patent US. Cl. 21021 16 Claims ABSTRACT OF THEDISCLOSURE -In the first stage of a continuous process oily sludges arernixed with light hydrocarbons differing substantially in specificgravity therefrom to separate the sludges into an oil-hydrocarbon phaseand a water-waxy solids phase. The oil-hydrocarbon phase is heated to atemperature above the critical temperature of the light hydrocarbons toremove the light hydrocarbons which are then recycled for mixing withadditional sludge and the oil is recovered for further use. Thewater-waxy solids phase is treated to obtain water of reduced ChemicalOxygen Demand which can be discharged in receiving bodies of waterwithout polluting the same. The waxy solids-water slurry which remainsis, in the second stage of the process of this invention, dried and theresulting dry waxy solids are treated with a light aromatic solvent,such as benezne, to yield a solution of wax and the aromatic solvent andwax-free solids. After the aromatic solvent wax solution is stripped toremove the aromatic solvent, a valuable wax product remains. In a finalstep, the Wax-free solids are heated to remove the last traces of thearomatic solvent therefrom yielding dry, hydrocarbon-free, solids whichare suitable for a wide variety of uses, such as, for example, for landfill.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a continuous two-stage process of deoiling, dewatering anddewaxing refinery sludges in which, in the first stage, the sludges aremixed with a light hydrocarbon followed by settling to give anoil-hydrocarbon phase and a water-waxy solids phase and in the secondstage, waxy solids separated from the water-waxy solids phase aretreated with an aromatic solvent to yield a wax-aromatic solvent extractfrom which the petroleum wax contained therein is recovered.

DESCRIPTION OF THE PRIOR ART The contents of sludges occurring inrefineries consists of sediments from the bottom of tanks, wastechemicals, emulsions, sand, clay, catalyst, rust generated oversometimes several years, as Well as Water and oil. The 'very nature ofthe contents has made it difficut over the years to economically deoiland dewater such sludges for reuse or for pollution-free disposal. Thus,the use of both benzene and naphthas with added Water in attempts todeoil sludges has been found economically unattractive because of thepoor settling characteristics of the resulting mass made centrifugingnecessary. Similarly, attempts to deoil and break sludges of the presenttype with iso-octane and a gas oil were also not successful because theoil phase and the water solids phase did not separate. Further, existingprocesses known in the tart have not provided any method for recoveringthe valuable wax product associated with the inorganic solids removedfrom such refinery sludges.

SUMMARY OF THE INVENTION It has now been discovered that by contactingrefinery sludges first with light hydrocarbons it is possible to ob-3,711,400 Patented Jan. 16, 1973 ice tain excellent phase separationwith attendant deoiling of the Waxy solids and separation of theoil-hydrocarbon phase from the water-waxy solids phase. On settling, thewater-waxy solids phase separates into a water phase of reduced ChemicalOxygen Demand (COD) and a waxy solids-Water slurry. Likewise, it hasbeen discovered that the waxy solids-water slurry can be dried and theresulting dry waxy solids treated with an aromatic solvent, such asbenzene, to yield a solvent-wax extract and wax-free solids. Strippingof the aromatic solvent from the waxsolvent solution yields valuablepetroleum products while heating of the wax-free solids yields a dry,hydrocarbonfree solids material suitable for a wide variety of uses, including land fill. In the first stage of this process centrifugation isnot required and settling and decanting effect separation of theoil-hydrocarbon from the water-waxy solids phase.

Light hydrocarbons suitable for use in the first stage of this inventioninclude aliphatic hydrocarbons such as propane, butane, pentane, as Wellas mixtures and isomers thereof. The volume ratio of the lighthydrocarbons to sludge on a liquid basis may range from about 3 to 1 toabout 20 to l and preferably from about 4 to 1 to about 8 to 1. Therecovered oil is clean and suitable for feeding to a catalytic crackingunit, or may be blended in fuel oils.

Light aromatic solvents useful in treating the waxy solids in the secondstage of this process include low molecular weight aromatics such asbenzene, toluene, xylene, ethyl benzene, cumene, isopropyl benzene,t-butyl benzene, mesitylene, etc. and mixtures and isomers thereof. Thevolume ratio of the :light aromatic solvent to the Waxy solids may bevaried over a Wide range, however, generally, it will be from about 5:1to about 30:1 and, preferably, from about 8:1 to about 20:1.

The petroleum wax recovered from the wax-aromatic solvent extract in thesecond stage of this process can be decolorized by the standardprocessing techniques of clay percolation and steaming etc., to yieldvaluable microcrystalline and distillate parafiin waxes. The dry,hydrocarbon-free solids recovered from the second stage of the processare suitable for land fill and a variety of other uses.

Further details of the subject process become more readily apparent fromthe following description taken together with the accompanying drawing,the single figure of which is a schematic view illustrating innon-limiting fashion a practical embodiment of the two-stage process ofthis invention.

DETAILED DESCRIPTION OF THE INVENTION As shown in the figure, refinerysludge and light hydrocarbon (i.e., light aliphatic hydrocarbon) fromline 3 are mixed in mixing area 1 from which they flow into a settlingarea, such as drum 5. Here the mixture of hydrocarbon and oil previouslycontained in the sludge flows to the top while the water and the waxysolids settle to the bottom. Upon further standing, the waterwaxy solidsphase separates to give a water phase and a waxy solids-water slurry.The water, which has a considerably reduced Chemical Oxygen Demand (COD)is taken off through line 19 for possible further reduction in COD in abiological section, such as an activated sludge tank.

The temperature in mixer 1 and drum 5 is maintained below the criticaltemperature of the light hydrocarbon, preferably at about 70 to F. andat a pressure of about 10 to about p.s.i.g. Maintaining a constant warmtemperature, for example, about 90 F. under sufficient pressurefacilitates separation of the phases in settling drum 5. a

The light hydrocarbon-oil top layer from settling drum is pumped throughline 6 by pump 7 into a heating area, such as heater 9, which issufliciently heated to raise the temperature of the stream above thecritical temperature of the particular light hydrocarbon 'which has beenused as a separating medium and generally this temperature will be about275 -390 F. Next, the hot, light hydrocarbon-oil mixture passes throughline 10 into a fractionating area such as tower 11, where an oil phasepoor in light hydrocarbon is taken 011? the bottom through line. while adense phase light hydrocarbon which is oil-poor comes off the topthrough line 3 for recycling and mixing with fresh sludge after coolingand depressurizing.. Wh'de the hydrocarbon is in residence in the heater9, line 10 and tower 11 sufiicient pressure is maintained thereon tokeep it in a dense phase, or about 500 to 600 p.s.i.g. The oil comingoff line 15 is substantially free of light hydrocarbon and can be sentto other portions of the refinery such as the crude stills or, afterstabilization for flash point, can be blended directly with fuel oil.Any light hydrocarbon lost in the process can be made up by addition tothe system through line 13.

In the second stage of the process of this invention as shown in thefigure, the water-waxy solids slurry passes through line 17 into drier21 where it is heated with steam entering through line 23, to effectremoval of the water and any light hydrocarbon which is exhaustedoverhead from drier 21 Via line 24. The dry, waxy liquid-inorganicsolids stream maintained at a temperature above about 200 F. is takenoif the bottom of drying tower 21 through line 25 and is sent to mixingarea 27 where it is mixed with recycle benzene entering the said mixingarea through line 29. The mixed materials then flow through the line 28into a settling area such as drum 31. From drum 31 the wax-aromaticsolvent solution is pumped by means of pump 48 through line 47 to asecond frac tionating area, such as stripping column 49. From the top ofstripping column 49 benezne for recycling to the process after coolingand condensing, is taken oif through line 53 while molten wax iswithdrawn through line 51 and sent to an appropriate recovery unit. Suchrecovery operations can include percolation through a clay bed followedby steaming to yield a decolorized microcrystalline wax, distillateparafiin wax, or a mixture of the two. Wax-free solids from settler 31are taken oif through line 33 and sent to drier 35 where the solids aresteamed to remove any trace of the aromatic solvent. Overhead from thedrier 35 there is taken off through line 39 a water-aromatic solventstream which is passed into a third distillation area, such as decanter41. Benzene taken off from decanter 41. as the overhead product via lineis recycled to mixing area 27 via line 29 after. cooling and condensingwhile water is withdrawn "from the dccanter 41 as the bottoms productvia line 43. Make-up aromatic solvent, as required, is added throughline 57. The dry, hydrocarbon-free, free-flowing solids leaving thedrier 35 are conveyed to an appropriate storage area or placed directlyon the land.

In the first step of the process in the heating and fnactionating areas,the operating conditions are as follows for the various lighthydrocarbons:

Tempera- Pressure,

Light hydrocarbons ture, F. p.s.i.g.

TABLE 1 Crude tank bottoms Sample sludge COD, mg. 0 /1 615, 000 Oil,weight percent. 24. 8-28. 7 Water, weight percent 20. 5 Ash, weightpercent 7. 35 pH 7. 5

Sludges of this type are non-uniform and it is ditficult to obtain arepresentative sample.

The following examples set forth various embodiments of the presentinvention and are to be considered not limitative:

EXAMPLE I 1,600 ml. of pentane was placed in a separatory funnel and 200grams of the Crude Tank Bottoms Sludge, described above, gravity onegram/ml. was added. After vigorous shaking, two phases appeared whichwere allowed to settle overnight. The clear top phase was decanted fromthe slurry bottoms. The bottom phase was vacuum filtered and thefiltrate combined with the top layer following which the pentane wasremoved by evaporation. Pentane and water were stripped from the filtercake by heating on a steam plate. The following was noted:

FIRST STAGE OF PROCESS 35A, stripped 35B, top layer dry sludge Sample(oil) layer Weight of product, grams 32 64 Yield, weight percent basischarge 16 32 Carbon, weight percent 59 Specific gravity, 50/60 F c 0.8772 Kinematic viscosity, F., cs l 11. 77

I 65.2 S.U.S.

SECOND STAGE OF PROCESS benzenebenzene- Sample (benzene-free) solublesinsolubles Weight recovered, grams 19. 8 4. 2 Weight percent, basischarge. 82. 5 16. 8 Melting point, F l 192 Carbon, weight percent l9. 9Ash, weight percent 81. 4

l Wax.

EXAMPLE II In this example, 1,600 ml. of n-pentane and 200 ml. of thesame Crude Tank Bottoms Sludge treated in Example I were added to aseparating funnel. The mixture was shaken vigorously, and the two phaseswhich formed were allowed to settle overnight. The clear, top layerweighing 857 grams was removed by decantation and the bottom layerremaining weighed 507 g. The following data were collected:

FIRST STAGE OF PROCESS Yield, weight percent basis charge Free carbon,weight percent Ash, weight percent- Specific gravity Gil/60 F. Kinematicviscosity, 100 F., es...

1 57.9 S.U.S.

SECOND STAGE OF PROCESS 25 grams of Sample 46C was extracted with atotal of 225 ml. of benzene at about 85 F. The benzene extract (i.e.,benzene-soluble phase) was separated from the solid benzene-insolublesphase by decantation. Evaporation of the benzene from thebenzene-solubles phase gave microcrystalline wax as the product.Pertinent data relating to the second stage operations are shown below:

benzenebenzene- Sample (benzene-free) solubles insolubles Weightrecovered, grams 18. 4 4. 8 Weight percent basis charge 73. 6 19. 2Melting point, F l 192 Carbon, weight percent 10. 8 Ash, weight percent-78. 5

1 Wax.

EXAMPLE III A total of 1,600 ml. of n-pentane and 200 grams of the samesludge sample employed in Example 1 were placed in a separatory funneland shaken vigorously for several hours after which the two phases whichseparated were allowed to settle overnight. The clear top phase (899 g.)were decanted from the bottom phase (375 g.) and both phases were heatedon a steam plate to evaporate the npentane and water. The followingobservations were made:

grams of Sample 690 was extracted with a total of 350 ml. of benzene atabout 80 F. The benzene-solubles phase was recovered by decantationfollowing which the benzene was removed by evaporation yielding amicrocrystalline wax. The benzene-insolubles phase was heated on a steamplate in order to remove benzene leaving behind a free-flowing,clean-looking, oil-free, solids product. Data relating to the secondstage operation are set out below:

benzene benzene- Sample (benzene-free) solubles insolubles Weightrecovered grams 11 3. 4 Weight percent, basis charge 73. 3 22. 7 Meltingpoint, F 1 190 Carbon, weight percent 23. 3 Ash, weight percent 67. 9

1 Wax.

The data in Examples I-III are summarized in Table 2 below:

TABLE 2 [Yield summarydeoiling, dewatering and dewaxing crude tankbottoms sludge-Basis charge, weight percent] Example I The difierencebetween the total and percent is due to the water rejected in Stage 1 ofthe process. This water would be returned to the biological section ofthe waste Water treating plants.

The recovered oil obtained in the first phase of the novel process ofthis invention is clean and suitable for incorporation in feed to acatalytic cracker, crude stills or it may be blended in fuel oils.

The deoiled and dewaxed solids are not oily to the touch and afterdrying are clean-appearing and free flowing. These solids are suitablefor land fill, etc., since unlike the sludge from which they arederived, they do not contaminate adjacent areas with oils as water-oilemulsions.

The high average recovery of oil obtained in the first stage makes itappear that the value of the oil alone may be sufficient to pay for theprocess and make it profitable.

Although in the examples in this specification the wax product recoveredis a microcrystalline wax, the method of this invention is notrestricted to the recovery of this particular type of wax. Sludgescontaining both distillate parafiin waxes including the normal paraifinwaxes, the isoparaffin waves and the naphthenic waxes as well asmicrocrystalline waxes together with mixtures of these two generalclasses of waxes can be efficiently processed using the method of thisinvention and high recovery of the valuable wax products containedtherein can be conveniently achieved.

What is claimed is:

1. A method for deoiling, dewatering and dewaxing sludges whichcomprises: (1) in a first stage mixing said sludges with a lightaliphatic hydrocarbon having a substantially lower specific gravity thansaid sludges, separating the resulting mixture into Water having areduced Chemical Oxygen Demand, a water-waxy solids slurry phase and anoil-aliphatic hydrocarbon phase, heating said oil-hydrocarbon phase to atemperature above the critical temperature of said aliphatic hydrocarbonunder a pressure sufficient to keep said aliphatic hydrocarbon in adense phase whereby said oil-aliphatic hydrocarbon phase is split intoan aliphatic hydrocarbon portion and an oil portion, recovering the saidaliphatic hydrocarbon and oil therefrom, and (2) in second stageseparating water from the water-waxy solids slurry, mixing the resultingwaxy solids phase with a light aromatic hydrocarbon solvent, separatingthe resulting mixture into a wax-aromatic hydrocarbon solvent phase andwax-free solids, and recovering the said wax from the wax-aromatichydrocarbon solvent phase.

2. A continuous process as defined in claim 1, wherein said aliphatichydrocarbon recovered from the oil-hydrocarbon phase is recycled formixing with additional sludge.

3. The continuous process as defined in claim 2, Wherein additionallight hydrocarbons are added to the recycled hydrocarbon.

4. The process as defined in claim 1, wherein said aliphatic hydrocarbonis selected from the group consisting of propane, butane, pentane andmixtures and isomers thereof.

5. The process as defined in claim 1 wherein the volume ratio of thealiphatic hydrocarbon to sludge on a liquid basis ranges from about 3:1to about 20:1.

6. The process as defined in claim 1 wherein the volume ratio of thealiphatic hydrocarbon to sludge on a liquid basis ranges from about 4:1to about 8:1.

7. The process according to claim 1 wherein said water which isseparated in the first stage is treated biologically to further reduceits Chemical Oxygen Demand.

8. The process as defined in claim 1 wherein said aliplltllatichydrocarbon is distilled from said oil-hydrocarbon p ase.

9. The process as defined in claim 1 wherein the light aromatichydrocarbon solvent is selected from the group consisting of benzene,toluene, xylene, ethyl benzene, cumene, isopropyl benzene, tertiarybutyl benzene, mesitylene and mixtures and isomers thereof.

10. The process as defined in claim 1 wherein the light aromatichydrocarbon is benzene.

11. The process as defined in claim 1 wherein the light aromatichydrocarbon is recovered from the wax-aromatic hydrocarbon solvent phaseby distillation.

12. The process as defined in claim 1 wherein the volume of the lightaromatic hydrocarbon solvent to the waxy solids ranges from about 5:1 toabout 30:1.

13. The process as defined in claim 1 wherein the volume ratio of thelight aromatic hydrocarbon solvent to the waxy solids ranges from about8:1 to about 20:1.

References Cited UNITED STATES PATENTS 2,039,636 5/1936 Dillon et al.210-71 X 2,730,190 l/l956 Brown et al. 210-84 X 2,078,992 5/ 1937 Bankset al. 210-71 X 2,724,731 11/1955 Finnlay 210-21 X 2,825,678 3/1958Jahnig et al. 210-21 X 3,368,876 2/1968 Bailey, Jr. 210-21 X 3,481,71312/1969 Titus 210-21 X JOHN ADEE, Primary Examiner US. Cl. X.R.

